Confirmed. I can send to Gmail but I can't send to my own domain hosted in Office 365. To clarify though: emails WILL send for me via the "test" tool built in to this plugin. However, other plugins (like Gravity Forms) will not work properly.
Thanks for posting this here, by the way. I've been fighting with WordPress for 2 hours now trying to figure out what was going on. Your comment put me on the right track.